Vaccination with recombinant NetB toxin partially protects broiler chickens from necrotic enteritis

Julian I Rood,Trudi L Bannam,Ricardo W Portela,Robert J Moore,Xuxia Yan,Kathy Sproat,Mark E Ford,Anthony L Keyburn

doi:10.1186/1297-9716-44-54

Abstract

NetB toxin from Clostridium perfringens is a major virulence factor in necrotic enteritis in poultry. In this study the efficacy of NetB as a vaccine antigen to protect chickens from necrotic enteritis was examined. Broiler chickens were immunized subcutaneously with purified recombinant NetB (rNetB), formalin treated bacterin and cell free toxoid with or without rNetB supplementation. Intestinal lesion scores and NetB antibody levels were measured to determine protection after mild oral gavage, moderate in-feed and heavy in-feed challenges with virulent C. perfringens isolates. Birds immunized with rNetB were significantly protected against necrotic enteritis when challenged with a mild oral dose of virulent bacteria, but were not protected when a more robust challenge was used. Bacterin and cell free toxoid without rNetB supplementation did not protect birds from moderate and severe in-feed challenge. Only birds immunized with bacterin and cell free toxoid supplemented with rNetB showed significant protection against moderate and severe in-feed challenge, with the later giving the greatest protection. Higher NetB antibody titres were observed in birds immunized with rNetB compared to those vaccinated with bacterin or toxoid, suggesting that the in vitro levels of NetB produced by virulent C. perfringens isolates are too low to induce the development of a strong immune response. These results suggest that vaccination with NetB alone may not be sufficient to protect birds from necrotic enteritis in the field, but that in combination with other cellular or cell-free antigens it can significantly protect chickens from disease.

Highlights

Necrotic enteritis in chickens is a common bacterial disease that costs the global poultry production industry an estimated US$2 billion annually [1]
RNetB induces a protective immune response To determine the immunogenicity of purified recombinant NetB (rNetB), chickens were immunized at day 7, boosted at day 17, and oral gavage challenged with EHE-NE18 at days 24 and 25
This study has evaluated whether NetB, a major virulence factor in necrotic enteritis, is an effective protective antigen when used as a subunit vaccine or as a supplement to either traditional bacterin or toxoid vaccines. rNetB alone was protective against a mild challenge with a virulent C. perfringens strain, but was not sufficient to protect against a heavy in-feed challenge

Summary

Introduction

Necrotic enteritis in chickens is a common bacterial disease that costs the global poultry production industry an estimated US$2 billion annually [1]. Ionophore anticoccidials or antibiotic growth promoters are used to control necrotic enteritis [2]. The risk of antibiotic resistance and consumer pressure has prompted the industry to reduce the use of in-feed antibiotics and it is likely that the use of ionophore anticoccidials will be reduced. In the European Union, the use of most antibiotic growth promotants has been banned, and necrotic enteritis remains an ongoing issue for producers in these countries [3,4]. This situation has increased the need to develop other

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Results

Conclusion